Hyperbaric and/or decompression chambers are used in many applications, and in many situations require the transfer of items either to and/or from the interior of the chambers. For example, deep sea diving, whether for pleasure or work, is associated with a serious risk of trauma to the divers. Without proper treatment, major problems from diving accidents, most commonly decompression sickness (or the “bends”) and Air Embolism, can lead to permanent disabling injuries and in some instances be fatal. Conventionally, offshore rig divers who work at great depths for considerable amounts of time must undergo decompression for extended periods time (e.g., up to two weeks). Normally the decomposition takes place in a conventional decompression chamber on the offshore rig or on a deck of a dive boat.
Dive chambers are examples of a category of pressure vessel referred to as a pressure vessel for human occupancy (“PVHO”). Once the divers are inside the vessels of the transfer system their condition must be kept stable. In keeping with this objective the problem arises of keeping the gas mixtures constant within the vessels of the transfer system. This includes both the pressures and concentrations of the compression gas, the breathing gas and the oxygen within the chamber. It is especially true for the oxygen supply within the vessel which must be replenished as it is used.
While the individual is in the decompression chamber, if medicines, supplies, food, drink, or other items are to be provided to the individual, a method and apparatus for supplying such items without substantially impacting the interior pressure and gas concentration inside the chamber needs to be provided. Additionally, it is desirable that in making this transfer that a minimum amount of interior gas pressure and/or gas concentration is lost.
One conventional method for providing access to the individual while inside the chamber is through an air lock which is independent of the entrance to the chamber. The air lock on a dive chamber can include a steel tube penetrating the chamber's wall. The steel tube can have doors called “closures” on each end.
Certain design conditions need to be addressed for an air lock or transfer portal to a decompression chamber. For example, in a portal with outer and inner doors, the outer door should be able to withstand the internal pressure of the dive chamber when the inner door is open.
In one embodiment a quick lock/quick unlock can be provided for the outer door. In one embodiment the quick lock/quick unlock for a small diameter portal can include a breech-lock type “two-ring” design familiar to those skilled in the art of quick opening closures. A two-ring style door can use a body ring welded to the body of the portal which rotatably houses a door. In one embodiment the door can have a plurality of radial extending protrusions. In one embodiment the body ring can have a plurality of enlarged openings which correspond to the plurality of radially extending protrusions of the door. In one embodiment the door can be rotated relative to the ring such that the plurality of radially extending protrusions slidable lock with the ring and prevent longitudinal movement of the door relative to the portal thereby keeping the door closed. In one embodiment the outer door can be rotated relative to the ring such that the plurality of radially extending protrusions enter the plurality of enlarged openings so that longitudinal movement of the door relative to the portal is allowable thereby allowing the door to be opened.
In one embodiment one or more of the plurality of radially extending protrusions can have a sloped section (in a rotational direction), such that when the outer door is rotated in the direction of slope the door tends to move in a longitudinal direction towards the interior of the portal. In this way the seal between the exterior door and the portal (such as an O-ring) can be more tightly sealed or energized. In one embodiment a perimeter groove in the ring can include a plurality of sloped sections such that when the outer door is rotated in a first direction the door tends to move in a longitudinal direction towards the interior of the portal causing a tighter seal to be made between the door and the portal. In one embodiment corresponding sloped areas are provided on both the plurality of radially extending protrusions of the exterior door and the plurality of sloped sections by the corresponding plurality of enlarged openings, such that both sloped portions tend to cause the door to more tightly seal against the portal when the door is rotated.
In some instances “three-ring” closures can be used on outer doors. In three-ring closures the door and body ring (first and second rings) do not rotate. Instead, a third ring (locking ring) located outside of the door and body rings itself rotates to engage mating lugs on the door and/or body rings and thereby obtain a seal. Two ring closures are preferred over three ring closures for various reasons: two ring closures are less expensive because they do not have a third ring; do not require lubrication of the sliding surfaces of this third ring; and do not have high stress areas hidden under such a third ring (which can inhibit a pre-failure detection analysis). Advantages of two ring versus three ring closures are particularly useful in competitive commercial applications such as dive chambers where they are subjected to harsh outdoor marine environments.
One hazard for conventional locks for closures is that the operator can attempt to open the air lock while the door is under pressure. As a consequence of this pressure differential, the door can be forced open very fast and the operator can be injured or the person inside the chamber can be injured by the inner door swinging open explosively.
Conventional locks for preventing two-ring closures from being opened while under pressure rely on indicators. Examples of “indicators” include pressure gages or pressure actuated spring loaded pop-up pistons. However, indicators only “notify/flag” operators, and depend on the operator recognizing and acting on the information provided by the indicators. Additionally, spring-loaded piston indicators retract when a small pressure still remains in the closure so that a false “OK” signal can be communicated. Even relatively small pressure differentials between the interior of the portals and the area where the closure is being opened can cause large forces on the closures and cause them to open fast causing injury.
Another potential problem with two-ring closures (or doors) relates to the door support allowing the door to both “swing out” (e.g., open and close) but also rotate about its axis (for locking/sealing and unlocking/unsealing). Because two distinct movements are required, a two-ring door hinge typically connects the door using a longitudinal bearing in the hinge blade which longitudinal bearing supports an axle in the center of the door. However, these bearings eventually wear, and such wear allows changes in concentric alignments of the door relative to the locking ring.
Alignment of the door relative to the locking ring is important because O-rings are preferred for sealing. O-rings (which are self-energizing gaskets) use the pressure of the fluid or gas being sealed to contribute to (or energize) their sealing effect. O-ring seals require containment in a cavity with limited gaps to prevent a form of failure referred to as “extrusion.” Extrusion failure of O-rings and the design gap sizes required to prevent it are described in O-ring design handbooks such as the “Parker O-Ring Handbook” and are familiar to those skilled in the art of O-ring joint design. For a closure where human life depends on its proper operation a concentricity misalignment of the door which leads to a gap and possible extrusion failure is unacceptable.
Conventionally available locks can be interlocks which are devices constraining the operator from opening the closure (door) until after the air locked has started to vent. Conventional interlocks for two-ring doors include threaded vent plugs in the door which vent plugs are chained to a stationary part of the vessel. These “vent-plug-on-chains interlocks” can restrict opening of the door, but they are slow and awkward.
Another problem with dive chamber air locks relates to the operation of the inner closure or door. Interior pressures of chambers are typically elevated compared to outside pressures. Because the inner door swings inwards when opening, the higher interior pressure of the dive chamber (or living space), compared to the pressure outside the chamber, causes the inner door to be pushed against the portal and pushed against a sealing O-ring (between the interior door and the portal). The force created by the higher interior pressure energizes the sealing O-ring, and seals the interior from the portal. Because of this higher interior pressure the inner door does not require a lock (or locking ring) to create a seal when in use and pressurized. However, dive chambers are not always in use and pressurized and when on ships, and when not pressurized dive chambers can be subjected to large jerking motions (such as wave action) causing the “unlocked” inner door to swing open and shut causing damage. Also, large motions can be seen during other activities of ships such as during the discharge if cargo which can cause an unlatched inner door to swing open and closed on its own. Additionally, dive chambers can be transported from one ship to another location such as by truck also subjecting the dive chamber to large jerking motions. During periods in which a dive chamber is subjected to large jerking motions, an “unsecured inner door” can bounce open and closed, which can cause damage to the inner door, O-ring, and/or portal.
Furthermore, if the inner door is somehow opened when the interior of the dive chamber is pressurized but unoccupied, a person standing outside the dive chamber would be unable to reach through the outer door and grab hold and close the inner door. However, even assuming that the interior door can be reached from the exterior, attempting to close the inner door from the exterior is very dangerous because the increased interior pressure can cause the interior door to slam shut very quickly, which slamming shut can harm the person attempting to close.
A seemingly simple solution for the interior door is to use a swing bolt latch or other clamping latch. However, swing bolts or clamping latches have the disadvantage of continuing to hold shut the inner door even where the portal pressure (or exterior pressure) is substantially greater than the interior dive chamber pressure. For example, locked swing bolts or clamping latches can trap elevated pressures inside the portal as the interior pressure of the dive chamber is reduced during a depressurization cycle. A trapped high differential pressure behind the inner door risks this door being slammed open and harming a person in the interior of the dive chamber—such as where the swing bolt or clamping latch is released (or fails) with a trapped high differential pressure behind the inner door. Such a condition could lead to an explosive release of the inner door.
Another disadvantage with conventionally available air locks (or access portals) is their lack of dealing with the time delay between: (a) starting the venting process of the interior of the portal and (b) the finishing of the venting process. Even where an interlock is used on the outer door to start venting and also “unlock” the outer door, a time lag exists between the start of the venting process to the time where the pressure differential between the interior of the portal and the exterior is at an acceptable level so that the outer door is not cause to explosively swing open.